(1) Field of the Invention
This invention relates to tire curing bladders, their manufacture and their use.
(2) Description of Related Art including information disclosed under 37 CFR 1.97-1.98
Pneumatic rubber vehicle tires are generally produced by building, molding and curing a green or uncured tire in a molding press. The green tire construct is pressed outwardly against a mold surface by means of an inner fluid-expandable bladder, commonly referred to as a curing bladder. By this method, the green tire is shaped against the outer mold surface which defines the tire tread pattern and configuration of the sidewalls. By application of heat and pressure via the curing bladder, the tire is molded and vulcanized at elevated temperatures.
Briefly, the proper selection of elastomers and compounding materials for the bladder formulation is essential in ensuring durability, required service life, and efficient curing bladder operation in a tire factory. Butyl rubber, e.g., isobutylene-isoprene copolymer, is the elastomer of choice in curing bladder formulations due to excellent heat aging resistance, good flex and tear resistance, and impermeability to air, inert gases, and water vapor. Fundamentally, this is due to the superior heat and steam resistance of cured butyl rubber and this has resulted in its wide use for high heat resistant applications.
Recently, there has been a global shortage of butyl rubber, creating a need to use less butyl rubber in the manufacture of curing bladders. There is also an ongoing need to improve the durability and service life of curing bladders, i.e., to extend the pull point of the curing bladder—bladder failure, when it occurs, can lead to the loss of up to six tires in a typical tire manufacturing process. There is also an ongoing need to improve heat transport through the bladder to improve the efficiency of the curing process and increase production rates on the vulcanization press.